1. Field of the Invention
Internal combustion engines operate under a wide range of temperatures including low-temperature stop-and-go service as well as high temperature conditions produced by continuous high speed driving. Stop-and-go driving, particularly during cold, damp weather conditions, leads to the formation of a sludge in the crankcase and oil passages of a gasoline engine. This sludge seriously limits the ability of the crankcase oil to lubricate the engine. In addition, the sludge tends to contribute to rust formation within the engine. The noted problems are compounded by lubrication service maintenance recommendations calling for extended oil drain intervals.
It is known to employ nitrogen-containing dispersants and/or detergents in the formulation of crankcase lubricating oil compositions. Many of the known dispersant/detergent compounds are based on the reaction of an alkenylsuccinic acid or anhydride with an amine or polyamine to produce an alkenylsuccinimide or an alkenylsuccinamic acid as determined by selected conditions of reaction.
It is also known to chlorinate alkenylsuccinic acid or anhydride prior to the reaction with an amine or polyamine in order to produce a reaction product in which a portion of the amine or polyamine is attached directly to the alkenyl radical of the alkenylsuccinic acid or anhydride. The thrust of many of these processes is to produce a dispersant having a relatively high level of nitrogen. The noted known processes generally result in the production of a dispersant reaction product typically containing from about 0.5 to 5% nitrogen. These dispersant additives exhibited a high degree of oil solubility and have been found to be effective for dispersing the sludge that is formed under severe low temperature stop-and-go engine operating conditions. However, it has become increasingly difficult to formulate lubricants with these additives which meet the present requirements with respect to the prevention or inhibition of the formation of varnish.
2. Description of the Prior Art
U.S. Pat. No. 3,155,685 discloses a step-wise method for preparing an ester lactone by reacting a 2-alkenylsuccinic anhydride in which the alkenyl radical has less than 32 carbon atoms with a monohydric alcohol to form a monoester-acid intermediate product, and further reacting this intermediate product in the presence of an acid catalyst to produce an ester lactone useful as a plasticizer.
U.S. Pat. No. 3,522,179 discloses esters of hydrocarbon-substituted succinic acid which are prepared by reacting a chlorinated polyolefin with maleic anhydride to form an intermediate hydrocarbon-substituted succinic anhydride and then reacting the intermediate with a glycol, such as neopentyl glycol, or polyethylene glycol to form an acid ester.
U.S. Pat. No. 3,778,371 discloses lubricant and fuel compositions containing N-hydrocarbyl-substituted quaternary ammonium salts prepared by reacting a high molecular weight aliphatic hydrocarbon halide with a tertiary amine.
U.S. Pat. No. 3,936,472 discloses a method for preparing alkyl lactone esters by reacting an alkenylsuccinic anhydride with an alcohol or thiol in the presence of an acid-reacting catalyst and optionally further reacting the alkyl lactone ester with an amine.